This invention relates to a hydraulic power and control system for an industrial machine, such as a hydraulically powered excavator or the like.
Hydraulic excavators conventionally utilize hydraulic cylinders to control the position of the main excavator boom, to control the position of the arm at the end of the boom, and to control the position of the bucket at the end of the arm. Also, a hydraulic motor is conventionally utilized to rotate the excavator body that carries the boom on the undercarriage and it is also known to use a pair of independently controlled hydraulic motors to drive the opposite tracks of the machine's undercarriage to propel and steer the machine. Typically, such hydraulic systems have been open center type systems.
Since more than one of the hydraulically powered functions on such excavators are normally being operated at the same time, it is necessary that the hydraulic systems have a relatively high flow capacity. For that purpose, it is known to provide a pair of hydraulic pumps to supply fluid pressure for the system, since the smaller pumps are more readily available and normally are cheaper per unit of capacity than a single large pump. Moreover, the smaller pumps can be independently replaced at a much cheaper cost.
While high flow capacity is a desirable feature generally, it can be a detriment when an excavator is being used in an operation that requires relatively slow, accurately controlled movement of the various functions, such as when an excavator is being used to lay pipe, or unload trucks, or operating in close proximity to a structure or workers.